SOLIDWORKS Simulation 2018 Focuses on Free Surface Flows

SOLIDWORKS Simulation 2018 Focuses on Free Surface Flows

The addition of free surface flows to SOLIDWORKS Simulation 2018 means you can simulate how water fills up this tank. (Image courtesy of Dassault Systèmes.)

Another SOLIDWORKS launch has come and gone, and this year has marked some big improvements for the SOLIDWORKS Simulation 2018 portfolio. One of the biggest additions of note is the new topology optimization tool for structural parts.

This tool gives users an optimal design for a part given its design space, loads, constraints and manufacturing methods. The discussion around this advancement could take up a whole article in and of itself, so we have written it here on Engineers Rule (click here).

But there is much more in the realm of simulation for SOLIDWORKS 2018 than topology optimization. Here you will learn about other tools Dassault Systèmes has added to the mix,including cyclic symmetry for computational fluid dynamics (CFD), free surface CFD flows, nonlinear safety factors and displacement controls for nonlinear analysis.

For more improvements to SOLIDWORKS Simulation 2018 not covered in this article, watch this video:

SOLIDWORKS Flow Simulation: Free Surface Flows and Sector Periodicity

According to Stephen Endersby, director of product portfolio management at SOLIDWORKS, one of the biggest simulation additions to this release is the ability to simulate free surface flows.

Any flow where fluids and gas interact is considered a free surface flow. Examples include anything from a half-filled gas tank to a canoe on a river.

The simulation assesses the interface between gases and liquids. The software also considers any solids that might be affecting the flow of either the gas or liquid. To properly assess the interface of the gases, liquids and solids, these locations will need a finer mesh than any bulk areas.

“When you look at energy, power and utilities, there are a lot of flows that are free flows,” said Endersby. “They are challenging to solve computationally so it took us a while to get there.”

The first step to start a free surface flow simulation is to set the water level. Then the workflow changes depending on internal or external flows.

The setup of a free surface flow changes depending on if it is internal or external. (Image courtesy of Dassault Systèmes.)

For internal flows, like the gas tank, the simulation will model how the fuel slushes around. The sneaky way SOLIDWORKS modeled this is by moving the gravity vector around while keeping the tank stationary.

“Changing the gravity is a little smoke and mirrors, but it is physically correct if you are only working with a single physics,” said Endersby. “For now, it is just a single physics so we can get away with moving the gravity. But in the future, we want to incorporate multiphysics so we will need to have a more rigorous setup.”

For external flows, like the canoe on the river, the engineer must first decide if modeling the bottom of the riverbed will be important to the simulation. In a deep river, the riverbed will likely have little effect; however, near the shore, where the canoe is tied up, this is a different story. In this simulation, you can’t really play with gravity to perform the simulation.Instead, the programmers set it up to change the velocity of the liquid. The liquid velocity can also be pulsed to create a wave effect.

Unfortunately, there is no automated way to set up the water level for floating objects. However, Endersby hopes to add a bouncy function in future releases. It would certainly improve the customer experience to not have to break out an equation every time something is floating. For now, users must rely on hand calculations and any macros they can get their hands on.

Additionally, the free flow function is currently incompatible with simulations containing transitions, rotations, porous media or fans. Endersby is pushing for these to be added in future releases.

To reduce the size of the model, the user has simulated only a quarter of the cylinder. The results can then be mirrored across the axis of symmetry. (Image courtesy of SOLIDWORKS.)

Another big addition to SOLIDWORKS Flow Simulation is sector periodicity, or as a structural engineer might call it, cyclical symmetry. This tool is used to cut down on the number of elements in a model.

Instead, the simulation focuses on a portion of the model that is cyclically symmetric. For this to work, the fluid must flow along the path of the axis of symmetry.

Sector periodicity should also be useful to those in the oil and gas or production industries.

Unfortunately,sector periodicity is currently not compatible for phase transitions, cavitation, high Mach and mixing simulations. Endersby hopes to see these functionalities in future releases.

An important note about the safety factor functions for nonlinear systems is that the user requiresa considerable amount of understanding about their part and its material makeup.

Endersby explains that for traditional materials, the default safety factor is typically all you need. The material is well known and contains homogeneous properties. In this case, you take the yield stress of the material and divide it by the measured stress to get your safety factor. You then optimize the part until said safety factor is at a desired level.

This isn’t true for brittle or nonlinear materials like composites and plastics. For these materials, the user must define a maximum stress value, as the material might yield before it fully breaks or snap before showing signs of failure.

“You want to make sure the part stays in a linear range of behavior,” said Endersby. “If it ratchets and becomes deformed, it will not go back to the original shape. To avoid this, set a maximum stress at a range where the material still acts linear.”

Another addition to SOLIDWORKS Simulation is the use of displacement controls for nonlinear parts. This tool helps to control the iteration when solving a part that experiences large deformations under small forces. The displacement control function ensures that the system won’t jump to a large displacement under a small increase in the force.

“Take a straw,” said Endersby. “You push it on one end and then it collapses. You get a small displacement at first. But as you increase the force, you eventually get one huge displacement. With displacement control, you can set how the system reacts to get a stable result. It controls the force so you don’t move too quickly.”

The system does this by defining a series of displacements and then calculating the force needed to achieve that displacement. This is alternative to increasing the force and hoping it will have a smooth linear displacement.

Other useful additions to SOLIDWORKS Simulation include:

Improved stress singularity detection in stress hotspot diagnosis

Single pin connector for multiple coaxial cylinders and hinge definitions

Ability to copy simulation features of a part or subassembly into a new study of the assembly

Importable features include material, element types, contact, connectors, fixtures, loads and mesh controls (which you can import individually or all at once)

Ability to export deformed geometry for CAE analysis in various CAE tools

Formats include Abaqus, STL, NASTRAN andnative SOLIDWORKS

Ability to exclude area from clamp force (used to simulate plastic part production with slides and undercuts)

For more on SOLIDWORKS Simulation 2018, check out Dassault Systèmes’ launch page.

About the Author

Shawn Wasserman (@ShawnWasserman) is the Internet of Things (IoT) and Simulation Editor at ENGINEERING.com. He is passionate about ensuring engineers make the right decisions when using computer-aided engineering (CAE) software and IoT development tools. Shawn has a Masters in Bio-Engineering from the University of Guelph and a BASc in Chemical Engineering from the University of Waterloo.